1. Field of the Invention
The present invention relates to a multi-core optical fiber.
2. Description of the Related Art
In recent years, the demand for networks keeps increasing. To continually accommodate the increasing demand, transmission-line-related technology with which it is possible to configure large-capacity optical communication networks is in need at present and in the future.
Examples of technology used for enlarging the capacity of a network include multi-core optical fibers. A multi-core optical fiber is configured so that a plurality of core portions are included in the one optical fiber. The following non-patent document indicates that it is possible to enlarge a transmission capacity by transmitting an individual optical signal in each of the core portions in a multi-core optical fiber: D. M. Taylor, C. R. Bennett, T. J. Shepherd, L. F. Michaille, M. D. Nielsen, and H. R. Simonsen, “Demonstration of multi-core photonic crystal fibre in an optical interconnect”, Electronics Letters, vol. 42, no. 6, pp. 331-332 (2006). The multi-core optical fiber disclosed in this document is a hole-structure optical fiber, which has been drawing attentions in recent years. In such a hole-structure optical fiber, a strong confinement of light in the core portions is realized by the large number of holes formed in the cladding portion. As a result, it is possible to configure the distance between the core portions so as to be shorter. Accordingly, it is possible to dispose a large number of core portions in a small cross-section area, and it is therefore possible to arrange the core portions with a high density.
Further, to enlarge the transmission capacity, it is desirable to use a multi-core optical fiber that operates in a single mode in a larger wavelength bandwidth. For example, in the case where the cut-off wavelength of a multi-core optical fiber is 1.53 micrometers, the multi-core optical fiber is able to perform a single-mode transmission in a wavelength bandwidth that is equal to or larger than 1.53 micrometers. Further, by configuring the cut-off wavelength so as to be 1 micrometer or 0.85 micrometer, each of which is even shorter, the multi-core optical fiber is able to perform a single-mode transmission in an even broader bandwidth. As a result, it is possible to further enlarge the transmission capacity.